"The proxy server is refusing connections" PLEASE HELP!?

I am using my sisters computer but my other computer when i try to go online it says that about the proxy and that 'Firefox is configured to use a proxy server that is refusing connections" and to check proxy settings to make sure they are correct. I don't know where to find my proxy server to... show more I am using my sisters computer but my other computer when i try to go online it says that about the proxy and that 'Firefox is configured to use a proxy server that is refusing connections" and to check proxy settings to make sure they are correct.

I don't know where to find my proxy server to check. How do i locate it or fix it so i can go online?

Huge thanks in advanced
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